High-frequency board, high-frequency package, and high-frequency module

ABSTRACT

A high-frequency board includes an insulating substrate, a first line conductor, a second line conductor, a capacitor, a first bond, and a second bond. The insulating substrate has a recess on its upper surface. The first line conductor extends from an edge of the recess on the upper surface of the insulating substrate. The second line conductor faces the first line conductor across the recess on the upper surface of the insulating substrate. The capacitor overlaps the recess. The first bond joins the capacitor to the first line conductor. The second bond joins the capacitor to the second line conductor, and is spaced from the first bond.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/088,258, filed on Sep. 25, 2018, which claims benefit of JapanesePatent Application No.: 2016/067616, filed on Mar. 30, 2016 which claimsbenefit of International Patent Application PCT/JP2017/012371, theentire contents of which are incorporated herein by reference in theirentireties.

FIELD

The present invention relates to a high-frequency board, ahigh-frequency package including the high-frequency board, and ahigh-frequency module.

BACKGROUND

As wireless communication devices including mobile phones are widelyused, these devices have increasingly higher frequencies to transmitincreasingly larger volumes of information at an increasingly higherspeed. A known high-frequency board includes a capacitor located betweenportions of a signal line to remove the DC voltage component thattransmits high-frequency signals (refer to WO 2009/119443).

A high-frequency board described in WO 2009/119443 includes a dielectricsubstrate, a signal line arranged on a surface of the dielectricsubstrate to transmit signals, and a capacitor mounted on a portionseparating the signal line on the surface of the dielectric substrate toelectrically connect the separated ends of the signal line.

The capacitor is mounted on the surface of the dielectric substrate, andjoined to the substrate with an electrically conductive bond, such assolder. When an increasingly smaller and shorter capacitor is joined tothe substrate with such a bond, the bond can extend across and connectthe separated ends of the signal line. The separated portions of thesignal line may be electrically connected through the bond and may beshort-circuited.

BRIEF SUMMARY Technical Problem

A high-frequency board according to one aspect of the present inventionincludes an insulating substrate, a first line conductor, a second lineconductor, a capacitor, a first bond, and a second bond. The insulatingsubstrate has a recess on its upper surface. The first line conductorextends from an edge of the recess on the upper surface of theinsulating substrate. The second line conductor faces the first lineconductor across the recess on the upper surface of the insulatingsubstrate. The capacitor overlaps the recess. The first bond joins thecapacitor to the first line conductor. The second bond joins thecapacitor to the second line conductor. The second bond is spaced fromthe first bond.

A high-frequency package according to another aspect of the presentinvention includes a board, a frame, and the high-frequency boardaccording to one embodiment of the present invention. The frame with athrough-hole surrounds an upper surface of the board. The high-frequencyboard is mounted in the through-hole.

A high-frequency module according to still another aspect of the presentinvention includes the high-frequency package according to oneembodiment of the present invention, a semiconductor element, and a lid.The semiconductor element is mounted on the upper surface of the board.The lid is joined to an upper edge of the frame to cover thehigh-frequency package.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a high-frequency board (with nocapacitor) according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of the high-frequency board (withno capacitor) according to the embodiment of the present invention.

FIG. 3 is an enlarged view of a main part of the high-frequency board(with no capacitor) according to the embodiment of the presentinvention.

FIGS. 4A to 4C are cross-sectional views of the high-frequency board(with no capacitor) according to the embodiment of the present inventiontaken along line A-A of FIG. 1 , having a rectangular recess in FIG. 4A,a tapered recess in FIG. 4B, and a stepped recess in FIG. 4C.

FIG. 5 is an enlarged view of a main part of the high-frequency boardaccording to the embodiment of the present invention.

FIG. 6 is a graph showing the impedance of the high-frequency boardaccording to the embodiment of the present invention.

FIG. 7 is a cross-sectional view of a high-frequency board according toanother embodiment having the same structure as the high-frequency boardof the embodiment of the present invention except including an embeddedcapacitor.

FIG. 8 is an exploded perspective view of the high-frequency board (withno capacitor) according to the other embodiment of the presentinvention.

FIG. 9 is an enlarged view of a main part of the high-frequency board(with no capacitor) according to the other embodiment of the presentinvention.

FIGS. 10A to 10C are cross-sectional views of an uppermost layer to alowermost layer of the high-frequency board (with no capacitor)according to the other embodiment of the present invention taken alongline B-B of FIG. 8 , having a rectangular recess in FIG. 10A, a taperedrecess in FIG. 10B, and a stepped recess in FIG. 10C.

FIG. 11 is a perspective view of a high-frequency package according toan embodiment of the present invention.

FIG. 12 is an exploded perspective view of the high-frequency packageaccording to the embodiment of the present invention.

FIG. 13 is a perspective view of a high-frequency module according to anembodiment of the present invention.

DETAILED DESCRIPTION

A high-frequency board according to an embodiment of the presentinvention will now be described with reference to the drawings.

High-Frequency Board Structure

FIG. 1 is a perspective view of a high-frequency board 1 according to anembodiment of the present invention. FIGS. 2 and 3 are explodedperspective views of the high-frequency board 1 according to theembodiment of the present invention. FIGS. 4A to 4C are cross-sectionalviews of the high-frequency board 1 according to the embodiment of thepresent invention taken along line A-A of FIG. 1 . FIG. 5 is an enlargedview of a main part of the high-frequency board according to theembodiment of the present invention. FIG. 6 is a graph showing theimpedance of the high-frequency board according to the embodiment of thepresent invention. FIG. 7 is a cross-sectional view of a high-frequencyboard according to another embodiment with the same structure as thehigh-frequency board of the above embodiment except having an embeddedcapacitor. In the figures, the high-frequency board 1 includes aninsulating substrate 2, a first line conductor 3, a second lineconductor 4, a capacitor 5, a first bond 6, and a second bond 7.

As shown in FIGS. 1 and 2 , the insulating substrate 2 is a laminate ofinsulating layers 2 a, 2 b, 2 c, 2 d, and 2 e formed from dielectricsubstances. The insulating substrate 2 is, for example, rectangular,with the dimensions of 4×8 mm to 15×30 mm as viewed from above and aheight of 1 to 10 mm. Each insulating layer in the insulating substrate2 is formed from a dielectric material. Examples of the dielectricmaterial include ceramic materials such as sintered aluminum oxide,sintered mullite, sintered silicon carbide, sintered aluminum nitride,and sintered silicon nitride, as well as glass ceramic materials.

The insulating substrate 2 has an upper surface (surface on which thecapacitor 5 is to be mounted) having a recess 21 formed through theinsulating layer 2 a. The recess 21 is, for example, rectangular asviewed from above with the dimensions of 0.2×0.4 mm to 2×10 mm. Asviewed from above, the recess 21 may also be elliptical or square, ormay be rectangular but have round corners. The recess 21 is, forexample, rectangular in a cross-sectional view with the dimensions of0.1×0.2 mm to 5×10 mm. In other words, the recess 21 has a depth of 0.1to 5 mm. The recess 21 may also be, for example, rectangular, tapered,flared, or stepped in a cross-sectional view.

The insulating layers 2 b, 2 c, 2 d, and 2 e each have, on their uppersurfaces, multiple ground conductors around the positions overlappingthe recesses 21 and at the positions overlapping the first lineconductor 3 and the second line conductor 4. These ground conductors areelectrically connected vertically through, for example, vias. In FIG. 2, the squares indicate the positions overlapping the recesses 21, whichare surrounded by the ground conductors. The lower surface of theinsulating substrate 2, or the lower surface of the insulating layer 2e, is covered by a lower surface ground conductor layer. The lowersurface ground conductor layer, which is also electrically connectedwith the ground conductors on the insulating layers through, forexample, vias, serves as a reference potential.

The lower surface ground conductor layer is, for example, rectangular asviewed from above with the dimensions of 0.1×0.2 mm to 2×10 mm. Thelower surface ground conductor layer is formed from, for example, ametal material such as tungsten, molybdenum, or manganese.

As shown in FIG. 3 , the upper surface of the insulating substrate 2, orthe upper surface of the insulating layer 2 a has the first lineconductor 3 extending from an edge of the opening of the recess 21 awayfrom the recess 21. The first line conductor 3 includes a firstelectrode pad 3 a, to which a first electrode 5 a of the capacitor 5 isto be connected, and a first line 3 b extending from the first electrodepad 3 a away from the recess 21. As viewed from above, for example, thefirst electrode pad 3 a is 0.2 to 2 mm long, and 0.2 to 2 mm wide, andthe first line 3 b is 0.5 to 20 mm long in a direction parallel to thedirection in which high-frequency signals are transmitted, and is 0.05to 20 mm wide in a direction perpendicular to the direction in whichhigh-frequency signals are transmitted. The first electrode pad 3 a andthe first line 3 b are both 0.01 to 0.1 mm thick. The first electrodepad 3 a and the first line 3 b are formed from, for example, a metalmaterial such as gold, silver, copper, nickel, tungsten, molybdenum, ormanganese, and may be formed on the surface of the insulating layer 2 aas a metallization layer by co-firing or metal plating.

The first electrode pad 3 a overlaps at least the lower surface groundconductor layer and the ground conductors on the insulating layers. Thefirst line 3 b also overlaps at least the lower surface ground conductorlayer and the ground conductors on the insulating layers. This structureallows the first electrode pad 3 a and the first line 3 b to form astrip line structure with the lower surface ground conductor layer andthe ground conductors on the insulating layers. This facilitatestransmission of high-frequency signals.

The insulating substrate 2 or the insulating layer 2 a has, on its uppersurface, the second line conductor 4 extending from an edge of theopening of the recess 21 away from the recess 21. The second lineconductor 4 includes a second electrode pad 4 a, to which a secondelectrode 5 b of the capacitor 5 is to be connected, and a second line 4b extending from the second electrode pad 4 a away from the recess 21.The second electrode pad 4 a faces the first electrode pad 3 a acrossthe recess 21 as viewed from above. As viewed from above, for example,the second electrode pad 4 a is 0.2 to 2 mm long, and 0.2 to 2 mm wide,and the second line 4 b is 0.5 to 20 mm long in a direction parallel tothe direction in which high-frequency signals are transmitted, and 0.05to 20 mm wide in a direction perpendicular to the direction in whichhigh-frequency signals are transmitted. The second pad 4 a and thesecond line 4 b are both 0.01 to 0.1 mm thick. The second electrode pad4 a and the second line 4 b are formed from, for example, a metalmaterial such as gold, silver, copper, nickel, tungsten, molybdenum, ormanganese, and may be formed on the surface of the insulating layer 2 aas a metallization layer by co-firing, or metal plating.

The second electrode pad 4 a overlaps at least the lower surface groundconductor layer and the ground conductors on the insulating layers. Thesecond line 4 b also overlaps at least the lower surface groundconductor layer and the ground conductors on the insulating layers. Thisstructure allows the second electrode pad 4 a and the second line 4 b toform a strip line structure with the lower surface ground conductorlayer and the ground conductors on the insulating layers. Thisfacilitates transmission of high-frequency signals.

As shown in FIG. 5 , the capacitor 5 is arranged across the first lineconductor 3 and the second line conductor 4 to overlap the recess 21.The first electrode 5 a of the capacitor 5 is electrically connected andfixed to the first electrode pad 3 a through the first bond 6, and thesecond electrode 5 b of the capacitor 5 is electrically connected andfixed to the second electrode pad 4 a through the second bond 7. Thecapacitor 5 is, for example, rectangular as viewed from above, with thedimensions of 0.3×0.4 mm to 2×4 mm and a height of 0.3 to 2 mm. Thecapacitor 5 is formed from, for example, forsterite, aluminum oxide,barium magnesium niobate, or barium neodymium titanate. The arrangementof the capacitor 5 across the first line conductor 3 and the second lineconductor 4, and being electrically connected and fixed to the firstline conductor 3 b and the second line conductor 4 b removes the DCcurrent component from high-frequency signals.

The first and second electrodes 5 a and 5 b are arranged on the lowersurface of the capacitor 5 (surface facing the upper surface of theinsulating substrate 2). The first electrode 5 a is electricallyconnected and joined to the first electrode pad 3 a through the firstbond 6. The second electrode 5 b is electrically connected and joined tothe second electrode pad 4 a through the second bond 7. The second bond7 is spaced from the first bond 6 across the recess 21. The first bond 6may be, for example, known solder such as Sn—Ag—Cu solder, Sn—Zn—Bisolder, or Sn—Cu solder. Similarly, the second bond 7 may be one ofvarious types of solder such as Sn—Ag—Cu solder, Sn—Zn—Bi solder, orSn—Cu solder.

The first and second bonds 6 and 7 are spaced from each other across therecess 21 between the first and second electrode pads 3 a and 4 a. Therecess 21 can leave the space between the first and second bonds 6 and 7despite any excessive amounts of the first and second bonds 6 and 7.This structure reduces the likelihood of contact between the first andsecond bonds 6 and 7. To downsize the high-frequency board 1 and thecapacitor 5, the first and second electrode pads 3 a and 4 a may bearranged closer to each other. This can increase the likelihood ofcontact between the first and second bonds 6 and 7, thus causingunintended connection or short-circuiting between them. However, therecess 21 between the first and second electrode pads 3 a and 4 a canreduce the likelihood of such contact between the first and second bonds6 and 7 and enables the high-frequency board 1 as well as the capacitor5 to be downsized.

The first and second electrode pads 3 a and 4 a each may be, forexample, spaced from the ends of the opening of the recess 21. Therecess 21 thus further reduces the likelihood of contact between thefirst and second bonds 6 and 7.

The recess 21 has round corners as viewed from above. The recess 21 canthus reduce stress around the recess 21 locally concentrating during themanufacture of the insulating substrate 2, or when the capacitor 5 isjoined to the first and second electrode pads 3 a and 4 a through thefirst and second bonds 6 and 7.

The recess 21 is longer in a direction perpendicular to the direction inwhich the first and second electrode pads 3 a and 4 a are aligned. Therecess 21 can thus reduce stress at the joint between the capacitor 5and the first electrode pad 3 a through the first bond 6, and the stressat the joint between the capacitor 5 and the second electrode pad 4 athrough the second bond 7 interacting each other when the capacitor 5 isjoined to the first and second electrode pads 3 a and 4 a through thefirst and second bonds 6 and 7.

The recess 21 is longer in the direction perpendicular to the directionin which the first and second electrode pads 3 a and 4 a are alignedthan the capacitor 5 in the same direction (the width of the capacitor5). The recess 21 can thus further reduce the likelihood of contactbetween the first and second bonds 6 and 7.

The first line 3 b and the second line 4 b are narrower in a directionperpendicular to the direction in which the first and second electrodepads 3 a and 4 a are aligned than the first and second electrode pads 3a and 4 a in the same direction. The capacitor 5 is firmly joined to thefirst and second electrode pads 3 a and 4 a through the first and secondbonds 6 and 7.

The capacitor 5 having the recess 21 at the bottom (in the directiontoward the insulating substrate 2) has a space to reduce the likelihoodof the electrostatic capacities increasing between the first and secondelectrode pads 3 a and 4 a, between the first and second electrodes 5 aand 5 b, and between the first and second bonds 6 and 7. The space canalso reduce the likelihood of the impedance decreasing as theelectrostatic capacities increase. Thus, the high-frequency board 1according to the embodiment of the present invention can adjust theimpedance between the first and second electrode pads 3 a and 4 athrough the capacitor 5 and the first and second bonds 6 and 7 to anintended value.

Such impedance matching is shown experimentally in the graph of FIG. 6 .The graph compares changes in impedance along the transmission linecorresponding to the period in which high-frequency signals aretransmitted between the structure with the recess 21 and the structurewithout the recess 21. In the graph, the horizontal axis indicates timeand the vertical axis indicates the impedance of transmitted signals.The broken line shows the results for the structure without the recess21 on the upper surface of the insulating substrate 2, and the solidline shows the results for the structure with the recess 21 on the uppersurface of the insulating substrate 2. In the graph in FIG. 6 , forexample, the impedance of the high-frequency signal transmission linehas a predetermined value of 100Ω between the first line conductor 3 andthe second line conductor 4 through the first and second electrode pads3 a and 4 a and the capacitor 5. Without the recess 21, the impedancerapidly decreased to less than or equal to 90Ω between 15 to 20 ps atthe transmission line where the capacitor 5 is mounted. However, withthe recess 21, the impedance was maintained greater than or equal to 95Ωat around 10 ps, where the impedance was the lowest. In other words,this structure reduces the likelihood of the impedance changing largely.The impedance thus deviates less from the predetermined value.

The structure described above allows the high-frequency board 1 with therecess 21 to leave the space between the first and second bonds 6 and 7despite any excessive amounts of the first and second bonds 6 and 7.This reduces the likelihood of contact between the first and secondbonds 6 and 7. In other words, the high-frequency board 1 can transmithigh-frequency signals in good conditions.

To downsize the high-frequency board 1 and the capacitor 5, the firstand second electrode pads 3 a and 4 a may be arranged closer to eachother. This can increase the likelihood of contact between the first andsecond bonds 6 and 7, thus causing unintended connection orshort-circuiting between the first line conductor 3 and the second lineconductor 4. The recess 21 between the first and second electrode pads 3a and 4 a can reduce the likelihood of such contact between the firstand second bonds 6 and 7 and enables the high-frequency board 1 as wellas the capacitor 5 to be downsized further, unlike the structure withoutthe recess 21.

The first and second electrodes 5 a and 5 b are arranged on the lowersurface and the side surfaces of the two ends of the capacitor 5. Thefirst electrode 5 a arranged on the side surface of one end of thecapacitor 5 is electrically connected and fixed to the first electrodepad 3 a through the first bond 6, and the second electrode 5 b arrangedon the side surface of the other end of the capacitor 5 is electricallyconnected and fixed to the second electrode pad 4 a through the secondbond 7. When the first and second electrodes 5 a and 5 b are eachcontinuously arranged on the lower surface and the side surfaces of thetwo ends of the capacitor 5, the capacitor 5 can be firmly connected andfixed to the first and second electrode pads 3 a and 4 a. With a lowerend portion of the capacitor 5 partially fitted in the recess 21, thefirst and second electrodes 5 a and 5 b arranged on the side surfaces ofthe two ends of the capacitor 5 can be connected and fixed to the firstand second electrode pads 3 a and 4 a.

In this case, the high-frequency board 1 has a height lower by the depthof the lower end portion of the capacitor 5 partially fitted in therecess 21 than when the capacitor 5 is arranged above the first andsecond electrode pads 3 a and 4 a (adjacent to the capacitor 5). Toallow the capacitor 5 to partially fit in the recess 21, the recess 21is tapered or stepped in a cross-sectional view. A lower end portion ofthe capacitor 5 is fitted in the recess 21 to easily create a spaceunder the capacitor 5 (adjacent to the high-frequency board 1).

The high-frequency board 1 according to embodiments of the presentinvention has the first and second electrode pads 3 a and 4 a eachcontinuously arranged on the upper surface of the insulating substrate 2to the two sides of the recess 21. The capacitor 5 is thus more firmlyconnected and fixed to the first and second electrode pads 3 a and 4 athrough the first and second bonds 6 and 7. This reduces the likelihoodof the capacitor 5 breaking or separating when the high-frequency board1 receives stress.

As shown in FIG. 7 , the first and second electrodes 5 a and 5 b may bearranged also on the upper surface of the two ends of the capacitor 5 aswell as on the lower surface and the side surfaces of the two ends ofthe capacitor 5. With the same advantage as described above, thecapacitor 5, with the electrodes arranged on its upper surface as wellas on its lower surface and the side surfaces of the two ends, can bemore firmly connected and fixed to the first and second electrode pads 3a and 4 a through the first and second bonds 6 and 7. With a lower endportion of the capacitor 5 partially fitted in the recess 21 asdescribed above, the first and second electrodes 5 a and 5 b arranged onthe upper surface as well as on the lower surface and the side surfacesof the two ends of the capacitor 5 can be connected and fixed to thefirst and second electrode pads 3 a and 4 a through the first and secondbonds 6 and 7.

In other words, the capacitor 5 can be electrically connected and fixedto the first and second electrode pads 3 a and 4 a to have its uppersurface lower than the upper surface of the insulating substrate 2 withthe first and second electrode pads 3 a and 4 a. In this case, thehigh-frequency board 1 can have a height lower by the height of thecapacitor 5 than when the capacitor 5 is arranged on the upper surfaceof the insulating substrate 2. When the capacitor 5 is fitted in therecess 21, the recess 21 is tapered or stepped in a cross-sectional viewas described above to create a space under the capacitor 5 fitted in therecess 21.

FIG. 8 is an exploded perspective view of the high-frequency board 1according to another embodiment of the present invention. FIG. 9 is anenlarged exploded perspective view of a main part of the high-frequencyboard 1 according to the other embodiment of the present invention.FIGS. 10A to 10C are cross-sectional views of the high-frequency board 1according to the other embodiment of the present invention taken alongline B-B of FIG. 8 . In the figures, the high-frequency board 1according to the above other embodiment of the present invention differsfrom the high-frequency board 1 according to the above embodiment of thepresent invention in that the high-frequency board 1 according to theabove other embodiment further includes an internal ground conductorlayer 22 at a position overlapping the recess 21. The internal groundconductor layer 22 has its edges overlapping the first and secondelectrode pads 3 a and 4 a as viewed from above.

As shown in FIGS. 8 to 10C, the first ground conductor layer 22 isarranged inside the insulating substrate 2, or specifically on the uppersurface of the insulating layer 2 c (surface facing the insulating layer2 b). The first ground conductor layer 22 is, for example, elliptical asviewed from above, and is partially connected to the ground conductoraround it through a connecting line conductor 24. The elliptical areahas the dimensions of 0.3×0.4 mm to 2×8 mm. The first ground conductorlayer 22 is shaped partially circular and rectangular.

Thus, the high-frequency board 1 according to the embodiment of thepresent invention can reduce cracks forming inside the insulatingsubstrate 2. Also, the first ground conductor layer 22 may be, forexample, arranged linearly continuous with the connecting line conductor24 as viewed from above. Thus, the high-frequency board 1 according tothe embodiment of the present invention can reduce stress inside theinsulating substrate 2.

The first ground conductor layer 22 and the connecting line conductor 24are formed from, for example, a metal material such as tungsten,molybdenum, or manganese, and may be formed on the upper surface of theinsulating layer 2 c as a metallization layer by co-firing. Inparticular, the first ground conductor layer 22 with curved edges likean ellipse as viewed from above can have less drastic changes inimpedance between the first and second electrode pads 3 a and 4 a thanthe first ground conductor layer 22 that is rectangular as viewed fromabove. This reduces insertion loss or reflection loss duringtransmission of high-frequency signals between the first and secondelectrode pads 3 a and 4 a through the capacitor 5 and the first andsecond bonds 6 and 7.

As shown in FIGS. 8 and 9 , the first ground conductor layer 22 overlapsthe recess 21. This structure further strengthens the electric fieldcoupling between the capacitor 5 and the ground conductor arrangedaround the capacitor 5 during transmission of high-frequency signalsthrough the capacitor 5 than the structure without the first groundconductor layer 22, thus reducing resonance possibly when the electricfield distribution expands more than intended during transmission ofhigh-frequency signals. With the electric field coupling with the firstground conductor layer 22, high-frequency signals can be smoothlytransmitted through the capacitor 5.

The first ground conductor layer 22 is arranged to allow the edges ofthe layer 22 to overlap the first and second electrode pads 3 a and 4 a.Like the advantage described above, this arrangement can strengthen theelectric field coupling between the first and second electrode pads 3 aand 4 a and the ground conductors arranged around the first and secondelectrode pads 3 a and 4 a when high-frequency signals are transmittedthrough the first and second electrode pads 3 a and 4 a. This can reduceresonance possibly when the electric field distribution expands morethan intended during transmission of high-frequency signals. With theelectric field coupling with the first ground conductor layer 22,high-frequency signals can be smoothly transmitted through the first andsecond electrode pads 3 a and 4 a.

As shown in FIG. 8 , the first ground conductor layer 22 is electricallyconnected to the ground conductor through the connecting line conductor24. Further, for example, the ground conductors arranged on the uppersurfaces of the insulating layers 2 b, 2 c, and 2 d are electricallyconnected through, for example, vias formed vertically through theinsulating layers.

As shown in FIGS. 1 to 3 and 5 , and FIGS. 8 and 9 , second groundconductor layers 23 are arranged on the upper surface of the insulatinglayer 2 a with the recess 21, the first line conductor 3, the secondline conductor 4, and the capacitor 5 between them. The second groundconductor layers 23 are arranged on the two sides of the first lineconductor 3 and the second line conductor 4, forming a coplanar line.This can strengthen the electric field coupling more than the strip linestructure. This also reduces expansion of the electric field,facilitating transmission of high-frequency signals.

The high-frequency board 1 according to the above other embodiment ofthe present invention accommodates electronic components electricallyconnected to the first and second electrode pads 3 a and 4 a across therecess 21. The electronic components include a resistor, an inductor,and beads in addition to the capacitor 5. The recess 21 creates a spacebetween the electrodes of the electronic components to reduce the effectof the electrostatic capacities between the electronic components andthe insulating layers 2 b, 2 c, 2 d, and 2 e, allowing the transmissionline of high-frequency signals to have an intended impedance.

Method for Manufacturing High-Frequency Board

The insulating substrate 2 including the insulating layers 2 a, 2 b, 2c, 2 d, and 2 e formed from, for example, sintered aluminum oxide may beprepared in the manner described below. An aluminum oxide-containingpowdery raw material is mixed with, for example, an appropriate organicbinder and an appropriate solvent to form slurry. The slurry is thenshaped into sheets using, for example, the doctor blade method, to yieldmultiple ceramic green sheets. The uppermost ceramic green sheet has athrough-hole, which is to be the recess 21.

The multiple ceramic green sheets are then cut or punched into anappropriate shape, and then stacked on one another and pressure-bonded.The stacked ceramic green sheets are then fired at a temperature of 1500to 1600° C. in a reducing atmosphere to complete the insulatingsubstrate 2.

The first electrode pad 3 a, the first line 3 b, the second electrodepad 4 a, the second line 4 b, the first ground conductor layer 22, thesecond ground conductor layer 23, the connecting line conductor 24, andthe ground conductors on the upper surfaces of the insulating layers areformed from, for example, a metallization layer, which may be formedfrom a metal having a high melting point, such as tungsten, molybdenum,or manganese, prepared in the manner described below. A metal powderwith a high melting point is kneaded with an organic solvent and abinder fully into a metal paste. The metal paste is then printed atpredetermined positions on the ceramic green sheets, to be the uppersurfaces of the insulating layers 2 a, 2 b, 2 c, 2 d, and 2 e, by, forexample, screen printing. These layers are then co-fired with theceramic green sheets. Through these processes, the metallization layersare applied to the upper surface and the interior of the insulatingsubstrate 2 or between the insulating layers to serve as the firstelectrode pad 3 a, the first line 3 b, the second electrode pad 4 a, thesecond line 4 b, the first ground conductor layer 22, the second groundconductor layer 23, the connecting line conductor 24, and the groundconductors on the upper surfaces of the insulating layers.

The vias may be formed in the manner described below. Through-holes arefirst formed in the ceramic green sheets to be the insulating layers 2a, 2 b, 2 c, 2 d, and 2 e. The through-holes are filled with the samemetal paste as for the first ground conductor layer 22, the secondground conductor layer 23, the connecting line conductor 24, and theground conductors on the upper surfaces of the insulating layers. Themetal paste is then co-fired with the ceramic green sheets. Thethrough-holes can be formed by, for example, die machining using a metalpin, or punching, for example, with laser. The metal paste may be easilyfilled into the through-holes using, for example, vacuum suction.

The insulating substrate 2 has, for example, a wall 13 on its uppersurface arranged on the first line conductor 3 or the second lineconductor 4. The wall is formed from the same insulating material as theinsulating substrate 2. Thus, the insulating substrate 2 is inserted andfixed to a through-hole 91 of a frame 9, which is formed from a metalmember described later, while being insulated from, for example, thefirst line conductor 3, the second line conductor 4, and the frame 9.

High-Frequency Package Structure

FIG. 11 is a perspective view of a high-frequency package 10 accordingto an embodiment of the present invention. FIG. 12 is an explodedperspective view of the high-frequency package 10 according to the aboveembodiment of the present invention. In the figures, the high-frequencypackage 10 includes a board 8, the frame 9, DC terminals 14 into which aDC voltage is input through lead members, and the high-frequency board 1according to an embodiment of the present invention.

The board 8 is rectangular as viewed from above, with the dimensions of10×10 mm to 50×50 mm and a height of 0.5 to 20 mm.

The frame 9 surrounds the upper surface of the board 8. The frame 9 isrectangular as viewed from above, with the dimensions of 10×10 mm to50×50 mm and a height of 2 to 15 mm. The frame has a thickness of 0.5 to2 mm.

The board 8 and the frame 9 may be formed from, for example, a metalsuch as iron, copper, nickel, chromium, cobalt, molybdenum, or tungsten,or an alloy of these metals, such as a copper-tungsten alloy, acopper-molybdenum alloy, or an iron-nickel-cobalt alloy. The metalmember for the board 8 may be prepared by processing (e.g., rolling orpunching) an ingot formed from such a metal material.

The frame 9 has through-holes 91 in its side walls. The high-frequencyboard 1 described above and DC terminals 14 are inserted into thethrough-holes 91 and fixed. In the high-frequency package 10, thehigh-frequency board 1 serves as input-output terminals forhigh-frequency signals, and the DC terminals 14 serve as terminals intowhich a DC voltage is input.

High-Frequency Module Structure

FIG. 13 is a perspective view of a high-frequency module 100 accordingto an embodiment of the present invention. In the figure, thehigh-frequency module 100 includes the high-frequency package 10according to an embodiment of the present invention, a semiconductorelement 11, and a lid 12.

The semiconductor element 11 is, for example, a laser diode (LD). Thesemiconductor element 11 may be, for example, a photodiode (PD). Thesemiconductor element 11 is arranged on a wiring board 15, andelectrically connected with an electrical connection member, such assolder or a bonding wire. For an LD semiconductor, another through-holemay be formed in the frame 9 to connect an optical fiber, in addition tothe through-hole 91 through which the high-frequency board 1 is to bemounted.

The lid 12 is joined to the upper edge of the frame 9 to cover thehigh-frequency package 10. The lid 12 is rectangular as viewed fromabove, with the dimensions of 10×10 mm to 50×50 mm and a height of 0.5to 2 mm. The lid 12 may be formed from, for example, a metal such asiron, copper, nickel, chromium, cobalt, molybdenum or tungsten, or analloy of these metals, such as a copper-tungsten alloy, acopper-molybdenum alloy, or an iron-nickel-cobalt alloy. The metalmember for the lid 12 may be prepared by processing (e.g., rolling orpunching) an ingot formed from such a metal material.

The present invention is not limited to the above embodiments, but maybe modified variously without departing from the spirit and scope of theinvention. Modifications contained in the claims can fall within thescope of the present invention.

Reference Signs List

-   1 high-frequency board-   2 insulating substrate-   21 recess-   22 first ground conductor layer-   23 second ground conductor layer-   24 connecting line conductor-   3 first line conductor-   3 a first electrode pad-   3 b first line-   4 second line conductor-   4 a second electrode pad-   4 b second line-   5 capacitor-   6 first bond-   7 second bond-   8 board-   9 frame-   91 through-hole-   10 high-frequency package-   11 semiconductor element-   12 lid-   13 wall-   14 DC terminal-   15 wiring board-   100 high-frequency module

The invention claimed is:
 1. A high-frequency board, comprising: aninsulating substrate including an upper surface and a recess extendingin a first direction on the upper surface; a first line conductorlocated on the upper surface of the insulating substrate; a second lineconductor facing the first line conductor with the recess therebetweenon the upper surface of the insulating substrate; and a ground conductorlayer on the upper surface of the insulating substrate, wherein theground conductor layer extending along the first line conductor and thesecond line conductor so as to be spaced from the first line conductorand the second line conductor and so as to be spaced from the recess onboth sides in the first direction of the recess, and wherein the firstdirection is a direction different from an extension direction of thefirst line conductor and the second line conductor, wherein in planview, a first end of the first line conductor ends at a first side ofthe recess or the first end of the first line conductor is spaced fromthe first side, and a first end of the second line conductor ends at asecond side of the recess or the first end of the second line conductoris spaced from the second side.
 2. The high-frequency board according toclaim 1, wherein the first line conductor comprises a first electrodepad, and a first line which extends from the first electrode pad, thesecond line conductor comprises a second electrode pad, and a secondline which extends from the second electrode pad, and a distance betweenthe first line and the ground conductor layer and a distance between thesecond line and the ground conductor layer are smaller than a distancebetween each end in the first direction of the recess and the groundconductor layer.
 3. The high-frequency board according to claim 2,wherein a length in the first direction of the recess is larger than alength in the first direction of each of the first electrode pad and thesecond electrode pad.
 4. The high-frequency board according to claim 2,further comprising: a capacitor overlapping the recess; a first bondjoining the capacitor to the first line conductor; and a second bondjoining the capacitor to the second line conductor, wherein a width inthe second direction of the recess is smaller than a dimension of partof the capacitor which part is located on an upper surface of the firstelectrode pad and/or the second electrode pad and protrudes from an endin the second direction of the recess.
 5. The high-frequency boardaccording to claim 1, wherein a second direction is perpendicular to thefirst direction, and a width in the second direction of the recess issmaller than a distance between an end in the second direction of therecess and the ground conductor layer.
 6. The high-frequency boardaccording to claim 1, wherein a shape of the recess is symmetrical withan imaginary line which passes through a center in a plan view of therecess and extends in the first direction.
 7. The high-frequency boardaccording to claim 1, further comprising: a capacitor overlapping therecess; a first bond joining the capacitor to the first line conductor;and a second bond joining the capacitor to the second line conductor. 8.The high-frequency board according to claim 7, wherein a dimension inthe first direction of the recess is larger than a dimension in thefirst direction of the capacitor.
 9. The high-frequency board accordingto claim 7, wherein a distance in the first direction between thecapacitor and the ground conductor layer is larger than a distance inthe second direction between the capacitor and the ground conductorlayer.
 10. The high-frequency board according to claim 1, furthercomprising: an other ground conductor layer overlapping the recess. 11.The high-frequency board according to claim 10, wherein an upper surfaceof the other ground conductor layer at a position overlapping the recessis covered with a ceramic material.
 12. The high-frequency boardaccording to claim 1, wherein the first line conductor comprises aplurality of first line conductors which are located in parallel witheach other, and parts of the ground conductor layer are located betweenthe plurality of first line conductors.
 13. The high-frequency boardaccording to claim 1, wherein the second line conductor comprises aplurality of second line conductors which are located in parallel witheach other, and parts of the ground conductor layer are located betweenthe plurality of second line conductors.
 14. A high-frequency package,comprising: a board; a frame located on an upper surface of the board;and the high-frequency board according to claim 1, joined to the frame.15. A high-frequency module, comprising: the high-frequency packageaccording to claim 14; a semiconductor element mounted on the uppersurface of the board; and a lid joined to an upper edge of the frame andcovering the high-frequency package.
 16. The high-frequency boardaccording to claim 1, wherein the recess includes a bottom surface. 17.The high-frequency board according to claim 16, wherein the first sideof the recess and the second side of the recess are perpendicular to thebottom surface.